Let
δ(x,s):=δs(x)=δ0(x−s)
Then we ask what is the analogue of Sturm-Liouville equation Ly=f when G(x,s)=δ(x,s)
So, if we define
L(x)=−xddx
we have
Lδ=δ.
Note that
xnn!δ(n)(x)=(−1)nδ(x),
∞∑n=0xnn!δ(n)(x)=δ(x)∞∑n=0(−1)n,
Borel/Abel summation of Grandi's series
δ(x)=2∞∑n=0xnn!δ(n)(x)
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